Method for blending and loading solid catalyst material into tubular structures

ABSTRACT

The present invention relates to a method for blending and loading solid material into vessels, such as into the tubes of shell and tube reactors, in a manner which maximizes compositional homogeneity and consistency of quantities and configurations of the blended solid materials. The solid materials comprise one or more solid catalyst materials, one or more solid inert materials, or blends thereof.

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Patent Application No. 61/283,833 filed on Dec. 9,2009.

FIELD OF THE INVENTION

The present invention relates to a method for blending and loading solidmaterial into vessels, such as into the tubes of shell and tubereactors, in a manner which maximizes compositional homogeneity andconsistency of quantities and configurations of the blended solidmaterials. The solid materials comprise one or more solid catalystmaterials, one or more solid inert materials, or blends thereof.

BACKGROUND OF THE INVENTION

Solid catalyst materials are used in a wide variety of chemicalmanufacturing processes and are typically loaded, poured, arranged, orotherwise placed in process vessels to form a reactor having one or morereaction zones. In the reaction zones, reactants are contacted with thecatalyst materials, under suitable reaction conditions, to producedesired products. Initially, a new reactor is loaded with fresh, newcatalyst materials, inert solid materials, and mixtures thereof, in acontrolled and pre-determined manner, to organize and form the necessaryreaction zones for the desired reactions and products.

After a period of operation, which varies depending on the reactants andoperating conditions, the catalytic activity of the catalyst materialsin the reactor diminishes to the point that operation of the reactor isno longer economically efficient or feasible. At this point, one or moreof the “spent” catalysts and other solid materials must be removed fromthe reactor, and new, fresh “charges” of catalyst and other solidmaterials must be loaded, poured and arranged in the reactor to re-formthe one or more reaction zones.

For example, shell-and-tube heat exchangers are commonly used as processvessels for containing reaction zones to perform certain chemicalreaction processes. Such shell and tube reactors, when operated on acommercial scale to perform oxidation reactions, typically have a verylarge number of elongated hollow tubes (e.g., 3,000 to 30,000) which aregenerally parallel with one another and collectively surrounded by ashell. The inner diameter of each tube is generally between 0.75 and 2.0inches, with a length of from about 10 to 60 feet, or more. Each of thetubes is in fluid communication with an inlet and an outlet for thepassage of reactants and other process fluids through the tubes (i.e.,through the “tube side” of the reactor vessel). Fluid may be circulatedthrough the shell side of the reactor vessel to heat or cool the tubesand their contents during operation, as desired. The shell-and-tubereactor may be vertically-oriented (i.e., with the tubes orientedvertically and the reaction fluids flowing upward, or downward, throughthe tube), or horizontally-oriented (i.e., with the tubes orientedhorizontally and the reaction fluids flowing horizontally through thetube side), depending on the desired reactions, the overall process, andthe environment in which the reactor is situated.

Various chemical reaction process configurations are also known in theart and may comprise two or more catalyst-containing shell-and-tube heatexchangers in series, optionally with intermediate feed addition pointsand/or intermediate heat exchangers. Examples of such series, or“tandem”, reactor systems are described for example in U.S. Pat. No.6,639,106 B1 and U.S. Pat. No. 7,038,079. Alternatively, processconfigurations comprising single reactor shell (SRS-type) reactors maybe utilized. SRS reactors are well-known in the art and are describedfor example in U.S. Pat. No. 6,384,274 B1 and U.S. Pat. No. 4,256,783.Process configurations comprising single reactors in tandem withSRS-type reactors may also be employed without deviating from the spiritof the present invention.

When used to perform catalytic reactions, each of the tubes of suchshell and tube reactors typically contains one or more solid catalystmaterials which are arranged in the same order, pattern or composition,from tube to tube, thereby collectively forming one or more reactionzones of the reactor. One or more solid catalyst materials are typicallymixed with one another, with one or more solid inert materials, or both,to obtain a more homogenous mixture of the desired solid materials, aswell as to create mixtures of solids which vary in catalytic activity.Furthermore, mixtures of one or more solid inert materials, without anyactive catalyst materials, may be used to fill at least a portion of thereactor tubes to create inert zones upstream, downstream or intermediateactive reaction zones containing one or more catalyst materials.

As discussed herein, the terms reaction “zone” and reaction “stage” aregenerally used to mean regions within a reaction vessel where chemicalreactions occur, while “inert zones” are regions in which no chemicalreaction is encouraged or catalyzed. More particularly, the termreaction “stage” is used to describe a region in which a specificdesired chemical reaction is performed, catalyzed or otherwise promoted.The term reaction “zone,” on the other hand, is used to describe aregion within which the conditions of reaction vary due to physical andoperational characteristics such as, but not limited to, catalyticactivity, reaction temperature, residence time, etc. There are multipletechniques for varying each of these characteristics which are generallyknown to persons of ordinary skill and some of which will be discussedin further detail hereinafter. It is also well-known in the art that oneor more inert zones may be formed for various purposes including, butnot limited to, quenching, pre-heating, controlled cooling, manipulatingreaction rates, etc. Furthermore, inert zones may be positionedupstream, downstream, or intermediate reaction zones, and inert zonesmay lie adjacent one another, as desired by practitioners in the field.

In accordance with the foregoing terminology, a particular reactionstage may comprise one or more reaction zones. For example, a reactionprocess which involves only one chemical reaction mechanism, such asdehydrogenation of ethane to form ethylene, would be said to occur in asingle reaction stage wherein ethane feed material is converted directlyto ethylene product. This reaction is often performed in the presence ofsuitable catalyst material, such as chromium-based, ornickel-alumina-based catalysts. The single reaction stage may comprise asingle reaction zone, for example, containing a single catalyst material(e.g., same composition, shape, size, dilution, etc.) and being operatedunder the same reaction conditions (e.g., the same temperature orpressure, or the same degree of catalyst density, etc.) throughout itsentire volume. In such a case, the reaction stage and reaction zone arecoexistent and the terms may legitimately be used synonymously.

Alternatively, the reaction stage of an ethane dehydrogenation processmay comprise more than one reaction zone, in each of which ethane isdehydrogenated, but which differ in other ways. For example, a firstreaction zone may be filled with 100% chromium-based catalyst, whereas asecond reaction zone may contain 100% nickel-alumina-based catalyst, oreven a mixture of chromium-based and nickel-alumina-based catalyst.Alternatively, the second reaction zone may contain the samechromium-based catalyst as in the first reaction zone and, instead,differ by being maintained at a different reaction temperature, or fedby an additional reactant feed. Thus, a dehydrogenation process forconversion of ethane to ethylene is typically described as having asingle reaction stage which may include one or more reaction zones,which may differ in a number of ways but in all of which the samechemical reaction mechanism occurs.

As another example, a two-stage catalytic reaction process forconversion of propylene to acrylic acid comprises a first reaction stagein which propylene is converted to acrolein and a second reaction stagewherein the acrolein from the first stage is further converted toacrylic acid. Typically, each reaction stage contains catalyst materialsuitable for catalyzing the desired reaction therein, such as amolybdenum-bismuth-iron-based catalyst for conversion of propylene toacrolein in the first reaction stage, and a molybdenum-vanadium-basedcatalyst for conversion of the acrolein of the first stage to acrylicacid in the second reaction stage. Additionally, as should now be clear,each of the first and second reaction stages may comprise one or moredifferent reaction zones which differ from one another, within eachstage, by the type, composition or strength of catalyst material,reaction temperature, etc. Furthermore, a type of short-handedterminology may be used wherein the catalyst composition present in thefirst reaction stage is referred to as “R1” catalyst and the catalystcomposition that is used in the second reaction stage may be referredto, similarly, as “R2” catalyst. Such terminology will be usedhereinafter.

Methods and apparatus for efficient removal of spent catalyst are known.Improvements to removal methods and apparatus continue to be developedto minimize damage to the tubes of the reactor vessel and the solidmaterials themselves. See, for example, the devices and methodsdescribed in U.S. Pat. Nos. 4,568,029, 4,701,101, 5,222,533, 5,228,484,6,182,716 and 6,723,171. A recently developed method and apparatus fordislodging and removing solid catalyst and other materials from thetubes of shell and tube reactors is described in European PatentApplication Publication No. EP1967260 and involves use of one or morehollow lances rotatably mounted on a movable carrier. The carrier ismoved vertically, while the lances are axially rotated. Downwardvertical movement of the carrier inserts the distal ends of the lancesinto the openings of the corresponding tubes of a vertically orientedshell-and-tube reactor vessel. Each hollow lance has a hard-tippeddistal end shaped for impacting and dislodging the solid materialsduring rotation of the lance as it is inserted further into the tube. Avacuum source is connected to each hollow lance for removal of dislodgedsolid materials.

Similarly, various methods and apparatus for loading solid catalystmaterials and inert materials into shell and tube reactors are known,all of which tend to involve and address the same general steps andissues. For example, an important preliminary step is the preparation ofreasonably homogenous mixtures of one or more solid catalystcompositions, with or without inert materials, which are suitable inquantity and quality for forming reaction zones in the shell-and-tubereactor vessel. The more homogeneous the solid mixtures are, the moreconsistent the reaction zones formed from these mixtures will be in eachtube of the reactor. The more consistent the reaction zones formed ineach tube, the more uniform the reaction conditions will be throughouteach reaction zone of the reactor, thereby ensuring efficient andpredictable reaction processes for making products of uniform quality.It is noted that perfect or statistical homogeneity need not beachieved. As long as the variability from tube to tube is minimized to areasonable degree, the overall efficiency of the reaction zones of thereactor will be achieved and economic operation of the reactor will bepossible. Of course, the closer to perfectly homogeneous the solidmaterials throughout a reaction zone, from tube to tube, the moreefficient and predictable will be the reactions which occur in thereaction zone.

Depending on the particular reaction or reactions, raw materials,process apparatus, desired products and operating conditions, amongother factors, one or more catalysts are selected having particularproperties including, but not limited to, composition, size, color,shape, purity, catalytic activity, surface area, temperature toleranceand mechanical integrity. Solid catalyst materials may be obtained frommultiple individual batch manufacturing processes and, therefore, whilethey have substantially the same properties, one or more of theseproperties may vary within acceptable ranges from batch to batch. Thus,it is often advantageous to blend solid catalyst materials with oneanother, and even with other non-catalytic solids as already mentioned,to produce a more homogenous mixture of solid materials having thedesired combination of properties and having each property to thedesired degree. It is most advantageous where such blending operationsproduce such mixtures of solid materials efficiently and consistently.

Various devices have been developed to accomplish reasonably homogenousblending of solid materials. U.S. Pat. No. 4,285,602 describes a gravityflow blending system for granular materials, such as granularthermoplastic resins (e.g., polyethylene pellets). The system shown inU.S. Pat. No. 4,285,602 also includes a dust collector and an outletport member for removing dust from the system. U.S. Pat. Nos. 4,907,892and 4,978,227 provide disclosures of apparati and methods for blendingsolid particulate material, such as plastic pellets, using pressurizedgaseous fluid for entraining the material and measuring the amount ofmaterial, by height or weight, so as to be able to equalize the freshfeed and withdrawal rates from the main vessel. U.S. Pat. No. 4,569,597describes an apparatus for efficiently and uniformly blending solids,such as powders or other granular materials. This apparatus has interiorbaffles and is rotated about an axis. U.S. Pat. No. 4,553,849 provides amethod and apparatus for blending solid particulate materials, such aspolymer pellets, using a plurality of conduits and optional baffles.

The blending of other solid materials, such as food products, detergentpowders, pharmaceuticals and metal parts, has been achieved particularlywell using combinatorial weighing methods and apparatus. However, it isnoted that achieving component homogeneity has not been the focus ofsuch technologies and, therefore, would not be expected from suchtechnologies. Generally, combinatorial weighing methods involveselecting a combination of articles whose total weight or number isclosest to a desired value, and is often accomplished using computeralgorithms along with sensors and feedback loop programming. See, forexample, U.S. Pat. Nos. 4,661,917, 4,858,708, 5,050,064, 5,962,816, aswell as devices and processes commercially available from Ishida ScalesManufacturing of Kyoto, Japan and Triangle Package Machinery Company ofChicago, Ill. Such combinatorial weighing methods and apparatus oftenhave vibration means to move the solid materials along through theapparatus. The blends produced by combinatorial weighing methods areknown for their consistency of composition with respect to each type ofcomponent, but not necessarily for homogeneity throughout each blend.For example, where each “blend” of cereal flakes and raisins canreasonably be expected to contain the same percentage of each component,from batch to batch, it is not necessarily assured that the cerealflakes and raisins will be homogeneously mixed with one another in eachblended batch.

Accurate and consistent measurement of the quantities of the variousmixtures of solid materials before beginning loading operationsfacilitates the consistent and sequential loading of the solid materialsinto the tubes of a reactor to achieve uniform arrangement of solidmaterials in the tubes. Sometimes the mixtures of solid materials areloaded into temporary holding vessels or containers, such as bins orbags. This simplifies and speeds the later step of loading the materialsinto the tubes of the reactor in a consistent, predetermined andsequential order using apparatus adapted for such purposes. In practice,many of the aforementioned apparati and methods for blending solidmaterials, including plastic pellets, powders and food items, arecoupled with known apparati and methods for producing multiple batches,or “charges,” of separately packaged, or bagged, homogenous mixtures ofsolid materials, each having the same quantity, for use in filling thereactor tubes in accordance with the predetermined schedule.

The homogenous mixtures of solid materials are loaded, poured, arranged,or otherwise placed in the tubes to form one or more reaction zones of aprocess vessel. As already described hereinabove, the reaction zonesdiffer from one another in one or more characteristics including, butnot limited to, catalytic activity, reaction temperature, residencetime, etc.

Each mixture of solid materials should be situated similarly in each ofthe tubes, i.e., the mixtures should be reasonably homogeneous comparedto one another and occupy a region of the same volume and position ineach tube, relative to other tubes. Clearly, where mixtures of solidcatalyst materials and/or inert materials are used to form the reactionzones, it is imperative that the mixtures of solid materials be asuniform and homogenous as possible to ensure consistent and predictablecatalytic activity and fluid flow throughout each reaction zone. Inother words, proper configuration of reaction zone(s) requires that thevarious mixtures of catalyst and/or inert materials are provided to, anddeposited in, each of the tubes in the same quantities, consistently, inpredetermined and sequential order, having consistent density andpacking ratios, relative to the other tubes. Furthermore, it is criticalthat each tube, or other compartment containing reaction zones, isfilled with solid materials in substantially the same amount andarrangement to ensure formation of reaction zones and inert zones, ofknown volume and shape and, thereby, consistent catalytic activity andfluid flow.

As is understood by persons of ordinary skill in the art, in order toachieve optimal reactor performance, it is not only necessary to haveuniform and homogeneous mixtures of solid materials, but it is alsonecessary to maintain the same arrangement from tube to tube byconsistently and uniformly placing these mixtures into each tube of thereactor in the same order and height, from tube to tube, to minimizetube-to-tube variability. A key variable impacting tube-to-tubevariability is the catalyst loading rate which can be measured andcontrolled. Much effort and research have been spent developing ways tocontrol the catalyst loading rate.

While it is, of course, possible to load solid materials, such ascatalyst and inerts, into reactor tubes by hand, such as, for example,by pouring the catalyst through a funnel, it is preferred to utilize amechanized loading apparatus, commonly referred to in the art as a“catalyst loader.” Catalyst loaders minimize tube-to-tube variability,and often will also provide a substantial increase in loading rate overmanual loading methods which shortens the time necessary to load andpack all of the tubes in a reactor. Examples of suitable catalystloaders include the single-tube loader described in U.S. Pat. No.5,626,455, which has a single tubular member for solid catalystdelivery, and the multi-tube loader disclosed in U.S. Pat. No.4,701,101, which has multiple tubular members for solid catalystdelivery to correspondingly aligned multiple tubes of a reactor vessel.Multi-tube catalyst loaders having vibrating compartments, chutes,trays, etc., such as those described in U.S. Pat. Nos. 4,402,643,6,132,157 and 6,170,670, are especially useful, not only because oftheir ability to simultaneously load multiple tubes, but also becausethe catalyst loading rate can be adjusted easily by changing thevibration frequency of the loader.

A well-known measure of catalyst loading rate is the “drop rate,” or“drop time,” of the catalyst. The drop rate is commonly measured inunits of seconds/liter of catalyst loaded. As is well known in the art,the optimal catalyst loading rate is one which best balances thecompeting goals of: (a) loading as quickly as possible to minimizereactor downtime, and (b) loading slowly enough to ensure uniformdistribution of the catalyst within the tubes. If particulate solids areloaded into a tube too quickly, the particles may collide and becomelodged within the tube (commonly known as “bridging”) at a locationabove their intended accumulation point.

Bridging of particulate solids in reactor tubes is typically accompaniedby a corresponding void below the “bridge” and results in less catalystbeing loaded into the tubes than intended and/or longer than expectedzone lengths. Such non-uniform filling of the tube will result inuncontrolled, variable packing density along the tube length and is tobe avoided. Uncontrolled variations in packing density may result in hotspots, significant tube-to-tube variability in performance, andgenerally lower product yields. Non-uniform filling can generally bedetected through measurement of actual zone length in a given tube vs.the target zone length (commonly referred to as “outage measurement”);generally an increase of more than about 5-10% increase in zone lengthvs. the target length is indicative of non-uniform filling.

Another common method for detecting non-uniform filling of tubes withsolids materials is to measure the pressure drop (dP) of a knownreference gas flow through that tube. U.S. Pat. No. 6,694,802 disclosesan example of a device used for simultaneously measuring dP throughmultiple catalyst-containing tubes. Many other devices operating onessentially the same principle are known. The measurement of dP may beperformed at any point in the loading process to ensure thattube-to-tube packing density is within acceptable limits. For example,it is common in the loading of SRS-type reactors to check dP after acompleting the placement of the first reaction stage within the reactor.Typically, variation in dP measurements is considered excessive when agiven tube is more than about 20% higher or lower than the averagemeasured pressure drop value. Typically the pressure drop of a giventube should not be more than 15%, for example not more than 10%, higheror lower than the average measured pressure drop value.

Additionally, if dP measurement of the tubes is employed, it will berecognized by persons of ordinary skill that it is not necessary, in allcases, to measure the pressure drop in every tube. Rather, a randomsampling of tubes will often be sufficient for quality control purposes.If a random sampling of tubes is used, not more than 25% of the tubesundergo dP measurement, such as for example, not more than 10%, or notmore than 5%, or even not more than 1% of the tubes, undergo dPmeasurement.

In some cases, a higher-than-expected pressure drop may result fromaccumulation of catalyst fines, dust, and/or tailings within a giventube, rather than from catalyst bridging. This situation may often becorrected by blowing a volume of pressurized dry gas (such as, forexample, 100-120 psig air or nitrogen) into one end of the tube, throughthe solid materials packed in the tube, and out the opposite end of thetube—thereby ejecting the unwanted particulates that may be restrictingflow. The degree of catalyst fines accumulation can often be minimizedby utilizing vibratory catalyst loaders comprising dust removal means,such as vacuum hoods, screening trays, and the like (see for exampleU.S. Pat. No. 6,132,157, U.S. Pat. No. 6,170,670 and US2006/0243342),which keep such dust and fines from entering the tubes during loading ofthe solid materials. In accordance with the method of the presentinvention, optional dust removal means may also be employed within thecombinatorial weighing system to further minimize dust contained in aparticular mixture of solid materials.

If indications of significant bridging, such as excessive pressure dropor longer than expected zone lengths, is identified for a given tube, itis necessary to remove sufficient solid materials (catalyst, inert,etc.) to eliminate the bridge and then to replace these removed solidswith fresh solid materials of the same composition. The avoidance ofbridging altogether is obviously preferable to the use of suchtime-consuming corrective measures. It is, therefore, the knowledge ofthe minimum drop rate (seconds/liter) that is key to the avoidance ofbridging during catalyst loading, as drop rates slower than the minimumwill also avoid bridging.

The quickest allowable drop rate that may be used without the occurrenceof bridging is dependent on many factors, most notably the size of thecatalyst particle relative to the inside diameter of the tube into whichit is loaded, the shape of the catalyst particle, andparticle-to-particle uniformity. Other factors that may affect theallowable drop rate include the density of individual catalystparticles, the surface finish (or roughness) of the catalyst particles,the friability of the particles, the tendency of the particles toagglomerate or self-adhere, and the tendency of the particles to absorbmoisture and swell. It will of course be apparent to persons of ordinaryskill that similar concerns apply to all mixtures of solid materials,including solid catalysts, inert materials, and blends thereof, whichmay be loaded into reactor tubes.

Given the many variables that affect the minimum drop rate, it is notsurprising that a wide range of drop rates have been disclosed in theart. For example, U.S. Patent Publication No. 2006/0245992 explains thatdifferent particulate solid geometries and sizes require differentminimum drop times. In particular, it is reported that 8 millimeterdiameter ceramic balls loaded into tubes of 25 mm inside diameterrequire a drop rate of not shorter than 30 seconds per liter, whereascatalyst rings of 8 mm diameter require twice the drop time of theceramic balls, or not shorter than 60 seconds per liter. Similarly, inU.S. Pat. No. 5,626,455, it is disclosed that 8 mm ( 5/16-inch)diameter×9.5 mm (⅜-inch) long silver-catalyst particles can be loadedinto ethylene oxide reactor tubes of between ¾″ and 2″ (19 mm-51 mm)inside diameter at a typical drop rate of 90 seconds/liter.

Given this wide variation in drop rates, the minimum particulate solidsdrop rate for a specific catalyst loading situation are typicallydetermined empirically, on a case-by-case basis, by simpletrial-and-error experimentation, as will be described in greater detailhereinafter in accordance with the present invention. This use ofexperimentation is especially preferred when catalyst blends—such asthose produced by the method of the present invention—are being loaded,because the drop rates for these blends will be most difficult topredict by other means given complex particle-to-particle interactions,such as those which might occur, for example, between a mixture ofvariable-geometry particles in a diluted catalyst charge.

The present invention addresses the above-described issues andrequirements by employing combinatorial weighing machines to blend andprepare distinct and separate batches, or charges, of mixed solidmaterials, each comprising at least one solid catalyst material or solidinert material, in predetermined amounts. The batches of mixed solidmaterials are collected and later loaded into the tubes of a tubularreactor to form the various desired reaction zones to perform thedesired chemical reactions.

SUMMARY OF THE INVENTION

The present invention provides a method for blending and loading solidmaterial into the tubes of a shell and tube reactor. The method involvesidentifying a packing schedule which lists the types and amounts ofsolid materials needed to form different batches of solid materials forarranging in the tubes and forming desired regions in the shell and tubereactor. Each of the batches comprises one or more materials selectedfrom the group consisting of: solid catalyst materials, solid inertmaterials, and blends thereof. The present method next requires using acombinatorial weighing machine to produce the different batches, and thetypes and amounts of solid catalyst materials and solid inert materialsblended for each batch of solid materials are selected based on thepacking schedule. Each of the batches of solid materials is collected ina plurality of containers, and each container contains the same amountand proportion of the one or more solid materials, where the amount isdetermined based upon the packing schedule. Each of said plurality ofcontainers comprises a total number of containers which is determined bythe number and size of the tubes of the shell and tube reactor.

In a particular embodiment, the present method includes loading thebatches of solid materials from each of the containers intocorresponding tubes of the shell and tube reactor, according to apredetermined order dictated by the packing schedule, to form thedesired regions within the reactor consistently and homogeneously.

Various embodiments are possible. For example, the combinatorialweighing machine may comprise adjustable vibrating means for changingthe rate at which solid materials are moved through the machine andblended with one another. The combinatorial weighing machine maycomprise dust collection means for collecting and removing dust from thesolid materials, thereby preventing unwanted accumulation of dust in thetubes of the shell and tube reactor.

The containers may be bags and a bagging machine may be used with thecombinatorial weighing machine to accomplish the step of collecting eachof the batches of solid materials in a plurality of containers.

The step of loading the batches of solid materials from each of saidcontainers into corresponding tubes of the shell and tube reactor isaccomplished using a solids loading machine having one or more tubularmembers aligned with corresponding tubes of the shell and tube reactor.

The method of the present invention may further be applied to load areactor for two-stage oxidation of an alkene to form a correspondingunsaturated carboxylic acid. In such an embodiment, a packing scheduleis selected which provides a list of types and amounts of materialsrequired to perform two-stage oxidation of an alkene to form acorresponding unsaturated carboxylic acid, and the desired regionscomprise a first reaction stage wherein the alkene is converted to anunsaturated aldehyde and a second reaction stage wherein the unsaturatedaldehyde is further converted to the corresponding unsaturatedcarboxylic acid. Furthermore, the first reaction stage may comprise atleast one catalyst comprising a mixed metal oxide and being capable ofcatalyzing the conversion of an alkene to an unsaturated aldehyde, andthe second reaction stage may comprise at least one catalyst comprisinga mixed metal oxide and being capable of catalyzing the conversion of anunsaturated aldehyde to an unsaturated carboxylic acid. Either or bothof the first and second reaction stages may comprise one or a pluralityof reaction zones.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention will be gainedfrom the embodiments discussed hereinafter and with reference to theaccompanying drawings, in which like reference numbers indicate likefeatures, and wherein:

FIG. 1 is a schematic elevational view of a single tube of a shell andtube reactor in which a 2-stage, 3-zone catalyst packing schedule hasbeen created using the method of the present invention;

FIG. 2A is a schematic elevational view of a single tube of a shell andtube reactor in which a 2-stage, 4-zone catalyst packing schedule hasbeen created using the method of the present invention;

FIG. 2B is a top plan view of a catalyst clip used to retain the solidmaterials in the tube of FIGS. 1 and 2A; and

FIG. 3 is a schematic representation of the combinatorial weighingmachine system with dust collector and bagger options which is used inaccordance with the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The method of the present invention is suitable for blending and loadingsolid materials into vessels, such as into the tubes of shell and tubereactors, in a manner which maximizes compositional homogeneity andconsistency of quantities and configurations of the blended solidmaterials. The solid materials comprise one or more solid catalystmaterials, one or more solid inert materials, or blends thereof.

More particularly, the present invention provides a method for blendingand loading solid material into the tubes of a shell and tube reactor.The method involves identifying a packing schedule which lists the typesand amounts of solid materials needed to form different batches of solidmaterials for arranging in the tubes and forming desired regions in theshell and tube reactor. Each of the batches comprises one or morematerials selected from the group consisting of: solid catalystmaterials, solid inert materials, and blends thereof. There may be oneor more types of solid catalyst materials, as well as one or more typesof inert materials. The desired regions are determined based on whattypes of products are desired and what starting materials are to beused, which, in turn, dictates what chemical reactions are to beperformed by the reaction process. All such selections and decisionsconcerning which processes, products and starting materials to use, arewell known and understood to practitioners in industry as persons ofordinary skill in the art who typically exercise such judgment on aroutine basis early in the process design stages.

The method according to the present invention uses a combinatorialweighing machine to produce the different batches, and the types andamounts of solid catalyst materials and solid inert materials blendedfor each batch of solid materials are selected based on the packingschedule. Each of the batches of solid materials is collected in aplurality of containers, and each container contains the same amount andproportion of the one or more solid materials, where the amount isdetermined based upon the packing schedule. Each of said plurality ofcontainers comprises a total number of containers which is determined bythe number and size of the tubes of the shell and tube reactor. Finally,the present method calls for loading the batches of solid materials fromeach of the containers into corresponding tubes of the shell and tubereactor, according to a predetermined order dictated by the packingschedule, to form the desired regions within the reactor consistentlyand homogeneously.

The method of the present invention is not limited to use with aspecific reaction process, but rather, may be utilized with any knownsolid particulate catalysts and/or solid inert materials in numerousreaction systems. Conventional examples of catalysts and theirassociated oxidation production processes to which the method of thepresent invention is applicable include, but are not limited to:

-   -   (1) a catalyst that comprises silver as an essential component        and is useful for production of ethylene oxide by oxidizing        ethylene in a gas phase (for example, JP-A-116743/1988,        JP-A-4444/1987, JP-A-329368/1993, JP-A-510212/1998, and        JP-A-84440/1993);    -   (2) a catalyst that comprises molybdenum, bismuth, and iron as        essential components, and is useful for production of        (meth)acrolein and (meth)acrylic acid by oxidizing propylene,        isobutylene, tert-butanol, and/or methyl tert-butyl ether in a        gas phase (for example, JP-A-13308/1975, JP-A-56634/1989,        JP-B-52013/1981, JP-B-23969/1981, and JP-A-76541/1984);    -   (3) a catalyst that comprises molybdenum and vanadium as        essential components, and is useful for production of acrylic        acid by oxidizing acrolein in a gas phase (for example,        JP-B-11371/1974, JP-A-85091/1977, JP-A-279030/1994, and        JP-A-299797/1996);    -   (4) a catalyst that comprises molybdenum and phosphorus as        essential components, and is useful for production of        methacrylic acid by oxidizing methacrolein in a gas phase (for        example, JP-B-33539/1985, JP-B-26101/1991, and JP-A-12758/1984);    -   (5) a catalyst that comprises vanadium and titanium as essential        components, and is useful for production of phthalic anhydride        by oxidizing o-xylene and/or naphthalene in a gas phase (for        example, JP-B-29056/1995 and JP-B-15176/1983);    -   (6) a catalyst that comprises molybdenum as an essential        component, and is useful for production of maleic anhydride by        oxidizing benzene in a gas phase (for example, JP-A-78/1987);    -   (7) a catalyst that comprises phosphorus and vanadium as        essential components, and is useful for production of maleic        anhydride by oxidizing n-butane in a gas phase (for example,        JP-A-167711/1998, JP-A-51573/1995, JP-A-115783/1993, and        JP-A-35088/1975);    -   (8) a catalyst that comprises molybdenum as an essential        component, and is useful for production of propylene, acrolein,        and/or acrylic acid by oxidizing propane in a gas phase (for        example, JP-A-316023/1997, JP-A-57813/1998, and        JP-A-120617/1998);    -   (9) a catalyst that comprises vanadium as an essential        component, and is useful for production of pyromellitic        anhydride by oxidizing durene in a gas phase; and    -   (10) other solid particulate catalyst used for a gas-phase        catalytic oxidation reactions by packing in a fixed-bed        shell-and-tube reactor.

The catalysts suitable for use in connection with the present inventionare not especially limited to the above solid particulate catalysts (1)to (10) used for a gas-phase catalytic oxidation reactions, but othersolid particulate catalysts used for other reactions such as, withoutlimitation, ammoxidation reactions, hydrogenation reactions, anddehydrogenation reactions are also suitable in accordance with thepresent invention.

For example, a catalyst that comprises a Group VIII noble metal, a GroupIA and/or a Group IIA component as essential components, and is usefulfor the oxidative dehydrogenation (ODH) of alkanes to alkenes (see U.S.Pat. No. 4,788,371), such as, for example, the conversion of propane topropylene (see U.S. Patent Publication No. US 2008/0177117).

Also, a catalyst that comprises gold and palladium as essentialcomponents, and is useful for the production of vinyl acetate monomer(VAM) by reaction of ethylene, oxygen, and acetic acid in the gas phase(for example, see U.S. Pat. Nos. 5,808,136, 5,859,287 and U.S. Pat. No.6,013,834).

More generally, for example but without limitation, commercial-scale,shell-and-tube type, catalytic reaction systems typically useparticulate solid catalysts and inert materials within their tubes.While the use of blended catalyst mixtures can provide the opportunityfor improved reactor productivity and yield, it has been quite difficultin practice to achieve mixtures of sufficient homogeneity to realizesuch benefits with large-scale commercial reaction systems. Whileperfect homogeneity need not be achieved, as previously understood inthe art, substantial homogeneity is required.

Reliable blending of solids is, in general, very difficult and knownmethods of mixing materials tend to fall far short of producing thedesired homogeneous mixtures. Homogenous blending of particulate solidsis especially difficult, even more so than the blending of powderedsolids.

It is noted that the terms “blend” and “mixture” are used hereininterchangeably to mean a quantity of solid materials that contains morethan one type of solid materials, such as, two or more catalysts whichdiffer in composition, activity, shape, size, etc., or at least onecatalyst and at least one inert material, or two or more inert materialswhich differ in composition, shape, size, etc. In accordance with thepresent invention, it should be understood that use of the combinatorialweighing machine(s) to produce various blends and mixtures of solidmaterials simultaneously accomplishes the combination of the desiredamounts of each type of solid material, as well as sufficient mixing ofthe solid materials without subsequent mechanical mixing or stirring ofthe solids after they are combined.

The bulk catalyst loaders known in the art for loading catalystmaterials into reactors, are not able to reliably blend mixtures ofsolid catalysts and/or inert solids to achieve sufficient homogenousreaction zones within reactor tubes.

Pre-blending of catalysts and or inert materials is potentially a bettersolution, but up to now has had to rely upon mechanical mixingmeans—such as stirring, tumbling, & vibrating—which are known to beinsufficient for achieving truly homogenous mixtures with particulatesolids; additionally, such mechanical mixing means also tend todamage/fracture/crumble catalysts and inerts, which are often brittleand/or friable, introducing catalyst fines/dusts into the catalystcharge and leading high to pressure drops within the reaction system.

Catalyst may be purchased from commercial suppliers prepackaged incontainers, such as plastic bags. As previously noted, catalyst which isprepackaged in this way allows for easier handling of catalyst and moreefficient loading of catalyst materials into reactor tubes. Typicalweight variability of such commercially available prepackaged charges isabout +/−5%, or roughly +/−120 grams per nominal 2000-gram chargeweight. This is an undesirably high level of weight variability and willresult in high tube-to-tube variations in reaction zone length,undesirable non-uniformity of reaction zone activities, and ultimatelydiminished reactor performance. Additionally, the manual process bywhich such prepackaged charges are prepared is time consuming, requiringbetween 1 and 10 minutes per bag. This can be a significant costcomponent of the catalyst purchase price when tens of thousands of bagsof catalyst are required to load a reactor. With additional care,repetitive weight measurement, and numerous adjustment steps(adding/removing a portion of catalyst to/from the container duringfilling), it is possible to reduce weight variability to +/−2%, orroughly +/−40 grams per 2000-gram charge weight; however, this stillrepresents significant tube-to-tube variation and the time required toprepare each bag is substantially increased, which results in highercatalyst costs which are, of course, passed on to the purchaser.

By using the combinatorial weighing and bagging machine system inaccordance with the method of the present invention, it is possible toachieve substantially lower weight variability than with manual baggingmethods, for example not more than +/−1% by weight variability based onthe total desired weight of each bag. As detailed in Example 1,2000-gram catalyst charges are produced in accordance with the method ofthe present invention having a weight variability within +/−3 grams, oronly about +/−0.2% weight variability. In addition, the method of thepresent invention is capable of performing this task at rates equal toor greater than 35 bags/minute. Thus, the method of the presentinvention provides an extremely cost effective means for obtaining bagsof catalyst which are suitable and ready for loading into the oxidationreactor. That is, the method allows for purchase of catalyst materialsin bulk, which is less costly than pre-bagged catalyst, and, byutilizing the method of the present invention, thousands of bags ofcatalyst with extremely low weight variability per charge may be rapidlyand cost-effectively produced.

Thus, applicants have discovered that the use of combinatorial weighingmachines, such as those typically used in the food packaging industry,can be successfully employed to produce such highly desirablesubstantially homogeneous particulate-solid blends. Additionally, wehave found that such blends can be produced quickly and efficiently, andcan be integrated into the catalyst handling process to yieldpre-measured, bagged catalyst charges suitable for use with knowncatalyst loaders.

Previously existing and used mixing technologies have not accomplishedsufficiently homogeneous blending of solid catalyst and inert materialswithout also damaging the catalyst or inert materials. Further, becauseit is weight-based, the method of blending with combinatorial weighingmachines is substantially less susceptible to errors resulting fromcatalyst agglomeration, inter-particle surface friction, or particleswelling due to moisture pickup. The net result of this method is thatit is now possible to produce an infinite number of particulate catalystblends to be used in optimized packing schedules for commercial scalereaction systems, such as the production of (meth)acrolein,(meth)acrylic acid, ethylene oxide, propylene oxide, vinyl acetatemonomer, etc.

Examples of combinatorial weighing machines that may be used inaccordance with the method of the present invention include machinesproduced by Ishida Co., Ltd of Kyoto, Japan; Yamoto Scale Co., Ltd ofAkashi, Japan; Package Machinery Co. of Stafford Springs, Conn. USA;Triangle Package Machinery of Chicago, Ill. USA; and Hassia-Redatron ofButzback, Germany. It is advantageous to install the combinatorialweighing system in a humidity controlled environment to minimize thepotential for moisture absorption by the catalyst particles, as this canlead to incremental weight gain and adversely affect the determinationof weights in the system scales.

The method of the present invention is described in further detailhereinbelow in the detailed examples wherein combinatorial weighingmachines are successfully used to reliably and consistently blendcatalysts and inerts of differing sizes, geometries, and particledensities to achieve substantially homogeneous mixtures.

EXAMPLES Example 1 Lot Blending Example

Ten lots of YX-38.52DU (“R1” type) oxidation catalyst, commerciallyavailable from Nippon Kayaku of Japan, were used in this example. Eachlot of catalyst comprised about 230 kg of catalyst pellets and wascontained in its own uniquely-numbered drum. Samples of approximately 80grams were taken from each drum (lot) and were independently tested in alaboratory-scale reaction system to determine propylene conversion. Forcomparison purposes, all samples were tested at constant conditions,using the same reaction temperature, pressure, space velocity,time-on-stream, propylene concentration, and propylene:air:steam feedratio. The results were as follows:

TABLE 1A Catalyst Drum Propylene Lot # Weight (kg) Conversion 87 23097.765% 123 230 97.765% 70 230 97.764% 36 230 97.761% 140 230 97.756% 18230 97.756% 157 230 97.747% 244 110 97.744% 175 230 97.744% 228 23097.743%

To achieve more uniform catalyst performance in the commercial-scalereaction system, these ten lots were blended together using aCombinatorial Weighing system according to the method of the presentinvention to produce 2,180 kg of a homogenous “R1Z1” catalyst mixture(100% catalyst pellets) for use in the first reaction stage (11) of theexample commercial-scale reactor illustrated in FIG. 1. This homogeneousR1Z1 catalyst mixture had a blended propylene conversion of 97.755%. Theobjective of this operation was to produce complete charges of catalystmixture with a target weight of 2040.6 grams/charge and to place eachcharge so produced into a sealed polyethylene bag. In this example,blending is enhanced by adjusting system settings to produce ahalf-charge (1020.3 grams) per scale cycle and to use 2 scale cycles perbag.

The combinatorial weighing system used in this example is shownschematically in FIG. 3. It is a Selectacom, Model A918H1RN, in-lineweigher with optional dust collection (100), in combination with a modelSB62PR vertical form/fill/seal (f/f/s) bagger (120); both machines areavailable from Triangle Package Machinery Company of Chicago, Ill. USAand are similar to those configured and adapted for packaging solidsfoods, such as dry cereals. As assembled, the left feed train (104, 105,106) and the right feed train (101, 102, 103) continuously supplymaterial to the top of weigher (100); weigher (100) surmounts the bagger(120) such that catalyst pellets move vertically downward through theweigher and exit as bagged charges (150 a, 150 b, 150 c) of catalystmixture from the bottom of the bagger. The entire system is configuredto use a single, common computer controller module (110). In thisexample, the computer controller (110) is adjusted to enable operationin the “single-product” mode.

Optional drum dumping units (not shown) were utilized in this example totransfer drums of catalyst into the two large feed hoppers (101, 104) atthe base of the combinatorial weighing system (five drums into eachhopper). For the purposes of clarity, material placed in hopper (101)will be referred to in this example as “Catalyst R” and material placedin hopper (104) will be referred to as “Catalyst L”.

Upon starting the system, the Left Feed Train and the Right Feed Trainoperated independently at speeds sufficient to maintain pace with theusage rate of the two catalyst streams. In this case, conveyors (102,105) continuously transferred catalyst pellets from each large feedhopper to two small hoppers (103, 106) at the top of the system. Anydust present was continuously removed from the hoppers and conveyors viaan optional integrated aspirating system (not shown). The small hoppers(103, 106) transferred catalyst pellets into a set of 9 vibratingfeeders (121, 122, 123, 124, 125, 126, 127, 128, 129), each adjustedindependently via controller (110) to operate at specific amplitude. Inthis example, the specific amplitude settings were as follows:

Feeder 121 122 123 124 - - - average amplitude 51 54 53 46 - - - 51Feeder 125 126 127 128 129 average amplitude 50 49 40 43 45 45.4

These vibrating feeders delivered catalyst pellets at rates dependent ontheir amplitude setting to accumulators (107 a, 107 b, 107 c, 107 d, 107e, 107 f, 107 g, 107 h, 107 i) with larger amplitude values delivering agreater quantity of catalyst pellets per unit time into the accumulatorsand smaller amplitude settings delivering a lesser quantity of catalystpellets per unit time into the accumulators; in this specific case, theleft side Feeders (121, 122, 123, 124) transferred pellets of Catalyst Linto four of the accumulators (107 a, 107 b, 107 c, 107 d) and the rightside feeders (125, 126, 127, 128, 129) transferred pellets of Catalyst Rinto the remaining five accumulators (107 e, 107 f, 107 g, 107 h, 107i). Because the vibrating feeders were set at range of amplitudesettings, rather than a single, identical amplitude setting, weightvariations were intentionally incorporated into each accumulator toenhance blending; through experimentation with the system, we havedetermined that a variation of only about 5 and 10% in the individualamplitude settings, relative to the average setting, is sufficient toprovide good results. It should also be noted that the average amplitudeof the four left side feeders (121, 122, 123, 124) should be greaterthan the average amplitude of the five right side Feeders (125, 126,127, 128, 129) to compensate for the differing number of feeders on eachside.

After being filled, each accumulator then simultaneously transferred itscontents into one of 9 scales (108 a, 108 b, 108 c, 108 d, 108 e, 108 f,108 g, 108 h, 108 i) directly below them, resulting in four scalescontaining Catalyst L (108 a, 108 b, 108 c, 108 d) and five scalescontaining Catalyst R (108 e, 108 f, 108 g, 108 h, 108 i). Afterdetermining the weight of pellets in each of the scales, the scalesdropped the material into 9 of 18 holders (109 a, 109 b, 109 c, 109 d,109 e, 109 f, 109 g, 109 h, 109 i, 109 j, 109 k, 109 l, 109 m, 109 n,109 o, 109 p, 109 q, 109 r); these steps were repeated a second time tofill the remaining 9 holders.

The computer controller (110) then selected an optimal subset of the 18individual weights, which when combined, achieves the closest match tothe target weight of 1020.3 grams. These selected holders then openedsimultaneously to release into discharge port (115) enough pellets tocreate a half-charge of catalyst; the release of pellets from theselected holders into the discharge port signifies the end of a singlescale cycle.

Additional catalyst pellets then moved through the accumulators andscales to refill the emptied holders and theweight-optimization-and-release step was repeated, signifying the end ofanother scale cycle. As previously stated, the system was configured inthis example to release a half-charge (1020.3 grams) of catalyst mixtureper scale cycle and to use 2 scale cycles per bag of catalyst mixture,thereby producing bags of catalyst mix with a target charge weight of2040.6 grams.

Below the weigher (100), the vertical f/f/s bagger (120) continuouslydrew polyethylene film from a supply roll (not shown), shaped it into anine inch (22.9 cm) diameter cylinder, vertically sealed the cylinder toform a tube, and then sealed the tube horizontally at the bottom edge toform a bag below discharge port (115). Controller 110 was programmed toproduce bags that were 12 inches (30.5 cm) in length, sufficient to holdthe desired charge volume. The formed bag was then filled with theaforementioned single blended charge of catalyst (130), the top wassealed horizontally, the finished bag of catalyst was cut free (theremaining edge becoming the bottom of the next bag) and the finished bagexited the bagger on a conveyor belt (140). Each successive finished bag(150 a, 150 b, 150 c) was visually inspected and manually placed into astorage drum (not shown). The system continued operating in thisfashion, producing over 1050 bagged catalyst charges at a rate of about35 bags/minute, until the large feed hoppers (101, 104) were emptied.

As this operation progressed, 8 finished bags were withdrawn from theconveyer belt at approximately 3.5 minute time intervals to serve asquality control samples. The contents of each sample bag wereindividually poured into a tared container and weighed.

TABLE 1B Bag # Weight (grams) Wt. % error 1 2037.55 −0.15 2 2037.35−0.16 3 2039.25 −0.07 4 2039.40 −0.06 5 2040.90 0.01 6 2039.40 −0.06 72037.40 −0.16 8 2039.90 −0.04

Table 1B compares the measured weights of the samples to the targetweight; it is evident from this data that the method of the presentinvention reproducibly provides catalyst charges with negligiblevariation in weights.

Although this example illustrates blending of lots in a single step, itis of course possible to utilize this same process to create multi-passblends in which the first blend is collected in a bulk container, ratherthan individual bags, and then recycled back to the feed hopper to besuccessively blended with additional material.

Example 2 Uniformity of Dilution Example

In accordance with the method of the present invention, a homogeneous“R2Z1” catalyst mixture (75 wt % catalyst pellets/25 wt % diluent) wasprepared for use in the second reaction stage of the examplecommercial-scale reactor. This R2Z1 catalyst mixture is to be placed inthe upstream zone of the second reaction stage (21) as illustrated inFIG. 1.

The same Combinatorial Weighing system described in Example 1 andillustrated in FIG. 3 was again used. The specific catalyst in thisexample was T-202.52XS3 (R2 type) and the diluent was IB-1000 5 mmdiameter inert spheres, both commercially available from Nippon Kayaku.

Catalyst, the majority component of the catalyst mixture, was placed inthe right side large feed hopper (101) at the base of the combinatorialweighing system and diluent, the minoroity component of the catalystmixture, was placed in the left side large feed hopper (104). Thescale's computer controller (110) was adjusted to enable operation inthe “two-product” mode and the target percentage of diluent was set to25%. Additionally, system settings were adjusted to produce a fullcharge (566.5 grams target weight) per scale cycle and to use 1 scalecycle per bag.

Upon starting the system, conveyors (102, 105) continuously transferredcatalyst pellets and diluent from the large hoppers to the two smallerhoppers (103, 106) at the top of the system. The Left Feed Train (104,105, 106) and the Right Feed Train (101, 102, 103) operatedindependently at speeds sufficient to maintain pace with the usage rateof the two streams. Any dust present was continuously removed from thehoppers and conveyors via an optional integrated aspirating system (notshown).

The small hoppers (103 & 106) transferred catalyst pellets into a set of9 vibrating feeders (121, 122, 123, 124, 125, 126, 127, 128, 129), eachadjusted independently via controller (110) to operate at specificamplitude. In this example, the specific amplitude settings were asfollows:

Feeder 121 122 123 124 - - - average amplitude 35 40 44 46 - - - 41.3Feeder 125 126 127 128 129 average amplitude 36 15 15 25 18 21.8

These vibrating feeders delivered catalyst pellets at rates dependent ontheir amplitude setting to accumulators (107 a, 107 b, 107 c, 107 d, 107e, 107 f, 107 g, 107 h, 107 i); in this specific case, the left sideFeeders (121, 122, 123, 124) transferred pellets of diluent into four ofthe accumulators (107 a, 107 b, 107 b, 107 d) and the right side feeders(125, 126, 127, 128, 129) transferred pellets of Catalyst into theremaining five accumulators (107 e, 107 f, 107 g, 107 h, 107 i). Becausethe vibrating feeders were set at range of amplitude settings, ratherthan a single, identical amplitude setting, weight variations wereintentionally incorporated into each accumulator to provide a widerrange of weight choices for the controller to select from, therebyimproving weight accuracy. Through experimentation with the system, wehave determined that setting the amplitude of a single vibrator withinthe five right side feeders to a value of between 1.5 and 2 times theaverage value provides especially good weight accuracy.

The accumulators then simultaneously transferred their contents into 9scales (108 a, 108 b, 108 c, 108 d, 108 e, 108 f, 108 g, 108 h, 108 i)directly below them, resulting in four scales containing diluent (108 a,108 b, 108 c, 108 d) and five scales containing catalyst (108 e, 108 f,108 g, 108 h, 108 i). After determining the weight of particulatematerial in each of the scales, the scales dropped the material into 9of 18 holders (109 a, 109 b, 109 c, 109 d, 109 e, 109 f, 109 g, 109 h,109 i, 109 j, 109 k, 109 l, 109 m, 109 n, 109 o, 109 p, 109 q, 109 r);these steps were repeated a second time to fill the remaining 9 holders.

The computer controller (110) then selected an optimal subset of the 18individual weights, which when combined, achieves the closest match tothe target weight of 566.5 grams total charge weight, whilesimultaneously providing the closest match to the required weight ratioof 424.875 grams of catalyst and 141.625 grams of diluent; theseselected holders then opened simultaneously to release into dischargeport (115) enough particulate solids to create a single blended chargeof catalyst. Additional particulate material then moved through theaccumulators and scales to refill the emptied holders and the weightoptimization and release cycle was repeated. As previously stated, thesystem was configured in this example to release a full charge (566.5grams) of catalyst mixture per scale cycle and to use just 1 scale cycleper bag of catalyst mixture.

Below the weigher (100), the vertical f/f/s bagger (120) continuouslydrew polyethylene film from a supply roll (not shown), shaped it into anine inch (22.9 cm) diameter cylinder, vertically sealed the cylinder toform a tube, and then sealed the tube horizontally at the bottom edge toform a bag below discharge port (115). Controller (110) was programmedto produce bags that were 8.5 inches (21.6 cm) in length, sufficient tohold the desired charge volume. The bagger operated as in the previousexample, discharging finished bags containing single, complete chargesof R2Z1 catalyst mixture onto the conveyor belt. Each finished bag wasvisually inspected and manually placed into a storage drum. Additionalcatalyst and diluent were added to the respective large feed hoppers asneeded to allow for long-term continued operation of the combinatorialweighing system. The system continued operating in this fashion, at arate of 25 bags/minute, until over 26,750 R2Z1 catalyst charges had beenproduced.

As this operation progressed, 15 sample bags were randomly withdrawnfrom the conveyer belt at regular time intervals.

Each sample (unopened bag) was weighed initially to determine the totalweight. The bag was then opened, the contents were poured out, and thediluent and the catalyst were hand-separated. The empty bag was weighedand the actual charge weight was calculated; the calculated chargeweight was then compared to the target charge weight of 566.5 grams(“Charge Wt Error”). Finally, the catalyst and diluent were individuallyweighed to determine blend accuracy (“Actual Weight, % Catalyst” and“Blend Error”).

TABLE 2 Measured Weights (grams) SEALED Calculated Measured WeightsActual Bag BAG BAG Charge Charge (grams) Weight % Blend # (TOTAL) ONLYWeight Wt Error CATALYST DILUENT Catalyst Error 1 576.17 9.79 566.38−0.02% 425.98 140.36 75.2% 0.3% 2 576.37 9.91 566.46 −0.01% 423.63143.15 74.7% −0.3% 3 576.27 9.91 566.36 −0.02% 425.05 141.72 75.0% −0.0%4 576.20 9.81 566.39 −0.02% 424.41 142.20 74.9% −0.1% 5 575.88 9.80566.08 −0.07% 426.95 139.30 75.4% 0.5% 6 577.22 10.10 567.12 0.11%425.33 141.77 75.0% 0.0% 7 576.85 10.06 566.79 0.05% 425.18 141.74 75.0%0.0% 8 577.24 10.20 567.04 0.10% 424.49 142.70 74.8% −0.2% 9 575.9210.00 565.92 −0.10% 424.35 141.96 74.9% −0.1% 10 576.85 9.93 566.920.07% 424.08 142.95 74.8% −0.3% 11 577.20 10.55 566.65 0.03% 424.97141.67 75.0% 0.0% 12 576.38 10.33 566.05 −0.08% 424.45 141.69 75.0%−0.0% 13 576.46 10.49 565.97 −0.09% 424.76 141.38 75.0% 0.0% 14 576.7510.54 566.21 −0.05% 424.38 142.00 74.9% −0.1% 15 576.80 10.46 566.34−0.03% 426.46 140.08 75.3% 0.4%

The data in Table 2 demonstrates that the measured weights of the samplecharges as compared to the target charge weight are within the range of+/−0.11%; Table 2 also shows that the blend error for the actualcatalyst mixture as compared to the 75% catalyst mixture target is notmore than about 0.5%. It is therefore evident from this data that themethod of the present invention (a) provides catalyst charges withnegligible variation in weights and (b) produces catalyst mixtures withnegligible variation in composition.

Example 3 Drop Test Example

As was previously stated, it is advisable that the minimum particulatesolids drop rate for a specific catalyst loading situation be determinedempirically, on a case-by-case basis, through the use of simpleexperimentation. This simple, iterative method is referred to as a “droptest” and can be performed by those of ordinary skill with the benefitof this disclosure.

In the specific case of this example, A ten-tube, vibratory catalystloader, of the type described in U.S. Pat. No. 6,132,157 (commerciallyavailable from Cat Tech of Deer Park, Tex.), was utilized to load testcharges of material (inerts or catalyst mixture) into a set number ofthe ten possible reactor tubes. The catalyst loader used in this exampleis one of several identical loaders in a set which are routinely used toload catalyst into commercial scale reactors. The loader comprises ahorizontal vibrating tray with ten sequentially numbered, parallellanes. These lanes are aligned with ten adjacent reactor tubes duringthe loading operation. For the purposes of this example, the catalystloader's lanes are sequentially numbered 1 through 10, with lanes 1 and10 being the outermost lanes located at the edge of the tray, and lanes5 and 6 being the innermost lanes, located in the center of the tray.These experiments were performed by placing the loader on the toptubesheet of a commercial-scale oxidation reactor with the same designand tube size (25 mm inside diameter) as the reactor to be loaded. Thedrop rate of material (catalyst, inert and/or mixtures thereof) in eachtest trial was controlled by adjusting the vibration frequency of theloader to a specific numbered setting using the loader's built-indigital controller. In this way, the exact settings for the particularcatalyst loader in use can be determined and recorded. As used herein,the term “drop time” refers to the elapsed time period that begins withthe first particle falling from the catalyst loader's tray into a givenreactor tube and ends when the last particle falls from the catalystloader's tray into that same reactor tube.

After each step in the testing, the “outage”—i.e., the topmost elevationof the accumulated material in the tube—is manually measured to verifythat the intended quantity of material and packing density has beenobtained.

In this example, eight identical 0.48 liter charges of R2Z1 catalystblend (prepared as previously described in Example 2) were used in fourconsecutive test drops. The target zone length for each test drop was1000 mm. It is desired that the variability of the average reaction zonelength as compared to the target is less than 3%. Additionally, it isdesired that individual tube reaction zone length values would not varymore than 0.5% from the average reaction zone length value. Data fromthese drop tests is summarized in Table 3 below.

Test Drop A

Based on previous experience loading catalysts, it was initially guessedthat a catalyst loader vibration setting of 40 might be an appropriatestarting point for testing. A first R2Z1 catalyst charge was transferredthrough Lane 1 of the loader in a total time of 56 seconds, which isequivalent to a drop rate of 118 seconds/liter. The resulting zonelength was determined to be 968 mm; as compared to the target length of1000 mm, this represented an average zone length variation of −3.2%.

Test Drop B

In order to reduce the average zone length variation, the controllersetting was adjusted to 47, which transferred the catalyst charge morequickly. More particularly, a second R2Z1 catalyst charge wastransferred through Lane 3 of the loader, with the controller setting on47, in a total time of 39 seconds, which is equivalent to a drop rate of81 seconds/liter. The resulting zone length was determined to be 984 mm;as compared to the target length of 1000 mm, this represented a reducedaverage zone length variation of −1.6%.

Test Drop C

In an attempt to further reduce the average zone length variation, thecontroller setting was next adjusted to 48, thereby transferring thecatalyst mixture just a little more quickly. In this test, a third and afourth R2Z1 catalyst charge were simultaneously transferred throughLanes 4 and 5, respectively, of the loader in a total time of 36seconds, which is equivalent to a drop rate of 75 seconds/liter. Theresulting average zone length was determined to be 981 mm; as comparedto the target length of 1000 mm, this represented an average zone lengthvariation of −1.9%. Because there were now two length measurements, itwas also possible to assess individual tube zone length variabilityagainst the average zone length value. In this case, the individualvariability was just 0.16%, which is well within the desired range ofnot more than 0.5%.

Test Drop D

A final test drop was performed, this time using four R2Z1 catalystcharges. The catalyst loader controller setting was maintained at thesetting of 48. Each of the four test charges were simultaneouslytransferred through Lanes 6, 7, 9, and 10, respectively, of the catalystloader in a time of 37 seconds, which is equivalent to a drop rate of 77seconds/liter. The resulting average zone length was determined to be975 mm; as compared to the target length of 1000 mm, this represented anaverage zone length variation of −2.5%. The individual tube variabilityas compared to the average zone length was not more than −0.37%, whichis well within the desired range (not more than 0.5%).

TABLE 3 Measured Calculated Loader Zone Tube Average Test ControllerDrop Drop Rate Lane Length vs. Average vs. Target Drop Setting Time secsec/liter # mm Zone Length Zone Length A 40 56 118 1 968 test A averagezone length 968 −3.2% B 47 39 81 3 984 test B average zone length 984−1.6% C 48 36 75 4 983 0.16% 5 979 −0.16% test C average zone length 981−1.9% D 48 37 77 6 972 −0.37% 7 976 0.12% 9 975 −0.04% 10 978 0.28% testD average zone length 975 −2.5%

As a result of this simple, iterative test method, it was determinedthat a drop rate of 77 seconds/liter was appropriate for uniform loadingof catalyst blend R2Z1 into the 25 mm tubes of the commercial shell andtube reactor. It was also determined that this drop rate could beobtained at a catalyst loader controller setting of 48.

Additionally, the individual data from this example illustrates thatmulti-tube vibratory catalyst loaders, wherein catalyst is conveyedacross a tray and into a series of adjacent tubes, may also experiencevariation in the drop rate across the lanes of the tray, with the outerlanes of the tray tending to drop the catalyst at a different rate thanthe lanes nearest the center of the tray.

Example 4 Catalyst Loading Example

A commercial-scale single reactor shell (SRS-type) oxidation reactor isto be used to produce acrylic acid from propylene. The specific SRSoxidation reactor of this example comprises over 25,000 identical tubes.FIG. 1 represents a single tube from this reactor, with a diameter of 1inch (25.4 mm) and a length of 26 feet (7925 mm).

As is well-known in the art, within an SRS-type reactor, propylene isconverted to acrolein in a first reaction stage, followed by theconversion of acrolein to acrylic acid in a second reaction stage. Inthis specific case, the example reactor is operated in an “upflow”configuration—that is, in operation, reactants will be introduced fromthe bottom of each tube and flow vertically upward; products will exiteach reactor tube at the top. Generally, in such a reactorconfiguration, the first reaction stage (R1) lies between the bottomtubesheet (1) and the intermediate tubesheet (15) in each tube; thesecond reaction stage (R2) lies between the intermediate tubesheet (15)and the top tubesheet (31) in each tube.

Based upon optimization studies performed in the pilot-plant reactionsystem, a three reaction-zone catalyst packing schedule was developedfor use in this example reactor (see FIG. 1). This three catalyst zonepacking schedule comprises a single catalyst zone for the first reactionstage (R1) and two catalyst zones of differing activity for the secondreaction stage (R2), with an interstage zone comprising solid inertmaterial positioned between the first and second reaction stages (R1,R2).

In the case of this specific example, two independently controlled flowsof nitrate cooling salt are circulated through the shell of the reactorto provide cooling to each of the reaction stages. In the R1 saltcirculation, cooling salt enters the lower portion of the reactor shellat a point above bottom tubesheet (1), flows around the tubes and exitsthe middle portion of the reactor shell at a point below intermediatetubesheet (15); in the R2 salt circulation, cooling salt enters themiddle portion of the reactor shell at a point above the intermediatetubesheet (15), flows around the tubes and exits the upper portion ofthe reactor shell at a point below the top tubesheet (31). Such aconfiguration is referred to as a co-current cooling salt circulation.

Given the sensitivity of acrylic acid yield to variations in processconditions such as temperature and reaction rate, it will be evident toone of ordinary skill in the art that it is necessary that the contentsof each of the over 25,000 tubes within this reactor are substantiallysimilar in the quantity, activity, and placement of catalysts.

Pre-blended charges of particulate solids material for each zone withinthe tube shown in FIG. 1 are prepared according to the method of thepresent invention, and are placed into bags for ease of handling, asdescribed in Examples 1 and 2. Each tube is to be loaded in thefollowing manner, to achieve the packing schedule illustrated in FIG. 1:

Beginning with empty tubes, the preheating zone is first assembled. Acatalyst clip (2) of the type shown in FIG. 2 b and commerciallyavailable from Deggendorfer Werft and Eisenbau GmbH of Germany is firstplaced at the bottom of each tube to hold the catalyst in-place withineach tube.

A multi-tube, vibratory catalyst loader, of the type described in U.S.Pat. No. 6,132,157 (commercially available from Cat Tech of Deer Park,Tex.), is utilized to simultaneously load charges of material (inerts orcatalyst mixture) into each of ten reactor tubes at one time. Althoughthis example focuses on the operation of a single catalyst loader, itwill be evident to one of ordinary skill that the task of loading tubesin a large reactor can be performed more quickly when multiple catalystloaders are employed at the same time. While the optimal number ofloaders that can be operated simultaneously will vary with the size ofthe reactor and the physical dimensions of the loader itself, it iscommon for between five and ten catalyst loaders to be operatedsimultaneously during catalyst installation. The drop rate of solidmaterial (catalyst mixture or inert) in each step is controlled byadjusting the vibration frequency of the loader to thepreviously-determined target value identified in drop testing. Aftereach step, the “outage”—or topmost elevation of the accumulated materialin the tube—is measured to verify that intended quantity of material andpacking density has been obtained. Measurement of pressure drop (“dP”)on a random sampling of tubes may also be performed to assuretube-to-tube uniformity. If either of these measurements indicates anappreciable error in loading, the non-compliant charge of material maybe removed and a fresh charge loaded to correct the error.

The aforementioned catalyst loader is used to place a layer of 218 gramsof inert material (6.4 mm diameter Denstone 57® catalyst bed supports,available from Norton Chemical Process Products Corp., of Akron, Ohio)on top of clip (2), to form preheating zone (3).

With the preheating zone (3) in place, the components of the firstreaction stage (R1) are then loaded. A charge of approximately 2040grams of “R1Z1” catalyst mixture is placed within each tube at a droprate of 65 seconds/liter to form a single catalyst zone (11) within thefirst reaction stage; this catalyst zone occupies the 3520 mm of tubelength directly above preheating zone (3). In this specific example,R1Z1 catalyst mixture comprises 100 wt % YX-38.52 DU catalyst,manufactured by Nippon Kayaku; preparation of R1Z1 charges has beenpreviously described in Example 1.

Next, using the vibratory catalyst loader, a charge of 272 grams of “IS”inert material is added to the tube at a drop rate of 167 seconds/liter;this inert material occupies the 500 mm of tube length directly abovesingle catalyst zone (11). In this specific example, the IS inertmaterial comprises 7.5 mm diameter by 6 mm long stainless steel Raschigrings.

Next, the second reaction stage (R2) is loaded. Again using thevibratory catalyst loader, two-catalyst zones (21 and 22) aresequentially loaded into each tube to form the second reaction stage. Abagged charge of approximately 566 grams of “R2Z1” catalyst mixture isplaced into the catalyst loader and transferred to the tube at a droprate of 77 seconds/liter to form catalyst zone (21) within the secondreaction stage; this catalyst zone occupies the 1000 mm of tube lengthdirectly above inert material (16). A bagged charge of approximately1281 grams of “R2Z2” catalyst mixture is then placed into the catalystloader and transferred to the tube at a drop rate of 69 seconds/liter toform catalyst zone (22) within the second reaction stage; this catalystzone occupies the 2240 mm of tube length directly above catalyst zone(21). In this specific example, R2Z1 catalyst mixture comprises ahomogenous blend of 75 wt % T202.52XS3 catalyst, manufactured by NipponKayaku, and 25 wt % 1B-1000 (5.2 mm diameter spheres) diluent, alsoavailable from Nippon Kayaku; preparation of R2Z1 charges has beenpreviously described in Example 2. R2Z2 catalyst mixture comprises 100wt % T202.52XS3 catalyst, manufactured by Nippon Kayaku, and wasprepared in essentially the same manner as used to prepare charges ofR1Z1 catalyst.

Finally, about 179 grams of inert material (32) is loaded on top ofcatalyst zone (22) by hand (although the aforementioned vibratorycatalyst loader could be used if desired); this inert material forms the“exit cooling zone” and generally occupies the 270 mm of tube lengthdirectly above catalyst zone (22). In this specific example, inertmaterial (32) comprises 6.4mm diameter Denstone 57® catalyst bedsupports, available from Norton Chemical Process Products Corp., ofAkron, Ohio.

A final measurement of dP on a random sampling of tubes is performed toassure tube-to-tube uniformity. The quantity of inert material (32) maybe increased or decreased, as appropriate, to provide a final adjustmentto the dP of the tube.

The repacked reactor was then put into commercial operation producingacrylic acid under the following operating conditions, whereby it wasdemonstrated that acrylic acid was produced stably, for a long time atexcellent yield:

propylene feed rate to the reactor=29,000 lb/hr;

7.3% propylene in the feed;

1.83 O2 to propylene ratio in the feed;

9.7% water in the feed;

reactor inlet pressure of 19.4 psig;

R1 salt temperature of 327.4 C;

R2 salt temperature of 287.3 C

At a time of 825 hours time on-stream (TOS), the performance of thisoxidation reactor was 86.2% overall acrylic acid yield at an overallpropylene conversion of 96.7%. The acrolein yield was 1.2%. From thisdata, it can be seen that the use of catalyst charges prepared inaccordance with the method of the present invention produces acrylicacid at excellent yield and high productivity.

Example 5 Rapid Blending & Bagging Operation

Based upon pilot-plant studies, a four zone catalyst packing schedule(see FIG. 2 a) was developed for use in another SRS-type commercialreactor for the production of acrylic acid from propylene. As previouslydescribed, propylene is converted to acrolein in a first reaction stage,followed by the conversion of acrolein to acrylic acid in a secondreaction stage. The four zone packing schedule of this example comprisedtwo catalyst zones of differing activity for the first reaction stage,and two catalyst zones of differing activity for the second reactionstage. ACF4 and ACS6 catalysts, available from Nippon Shokubai ChemicalLimited (NSCL) of Japan were utilized in this example reactor.

In this specific case, the example reactor comprised over 25,000 tubesand was operated in an “downflow” configuration—that is, in operation,reactants will be introduced from the top of each tube and flowvertically downward; products will exit each reactor tube at the bottom.Generally, in such a reactor configuration, the first reaction stage(R1) lies between the top tubesheet (201) and the intermediate tubesheet(215) in each tube; the second reaction stage (R2) lies between theintermediate tubesheet (215) and the bottom tubesheet (231) of eachtube.

In the case of this specific example, two independently controlled flowsof nitrate cooling salt are circulated through the shell of the reactorto provide cooling to each of the reaction stages. In the R2 saltcirculation, cooling salt enters the lower portion of the reactor shellat a point above bottom tubesheet (231), flows around the tubes andexits the middle portion of the reactor shell at a point belowintermediate tubesheet (215); in the R1 salt circulation, cooling saltenters the middle portion of the reactor shell at a point above theintermediate tubesheet (215), flows around the tubes and exits the upperportion of the reactor shell at a point below the top tubesheet (201).Such a configuration is referred to as a counter-current cooling saltcirculation.

Each tube is to be loaded in accordance with the packing schedulesummarized in FIG. 2 a and described herein. A catalyst clip (232) ofthe type shown in FIG. 2 b and commercially available from DeggendorferWerft and Eisenbau GmbH of Germany is first placed at the bottom of eachtube to hold the catalyst in-place within each tube. A layer of 232grams of ⅜″ diameter spherical ceramic balls is then placed on top ofclip (232), forming the cooling zone (233). Next, 1395 grams of R2Z2catalyst mixture (222) is placed on top of cooling zone (233). On top ofthe R2Z2 catalyst mixture (222) is next placed a layer of 616 grams ofR2Z1 catalyst mixture (221). Next is placed a layer of 635 grams of¼″¼″×0.03″ wall thickness stainless steel Raschig rings, forming theInterstage zone (216) for this particular packing schedule. Aboveinterstage zone (216) is placed a layer of 986 grams of R1Z2 catalystmixture (212). Finally, a layer of 447 grams of R1Z1 catalyst mixture(211) is placed on top of the R1Z2 catalyst (212) to complete thefilling of the tube.

In order to minimize the downtime associated with loading catalyst intoeach of the over 25,000 tubes in this specific reactor, a multi-tube,vibratory catalyst loader, of the type described in U.S. Pat. No.6,132,157 (commercially available from Cat Tech of Deer Park, Tex.), isutilized to simultaneously load charges of material (catalyst mixture orinerts) into each of ten reactor tubes at one time. To facilitate theoperation of the catalyst loader, individual charges of catalyst,raschig rings, and ceramic balls are prepared in advance using themethod of the present invention and are placed into individual sealedbags for ease of handling. Table 4 summarizes the activity involved inthe use of a combinatorial weighing system in accordance with theinventive method:

TABLE 4 Number Average of Bags Charge Charge Produced weight DescriptionR1Z1 26,300 447 grams 66 wt % ACF4 catalyst (NSCL); 34 wt % ¼″ × 3/16″cylindrical diluent R1Z2 25,880 986 grams 100% ACF4 catalyst (NSCL)Interstage 26,000 635 grams ¼″ × ¼″ × 0.03 wall thickness, zone 410stainless steel R2Z1 26,080 616 grams 86 wt % ACS6 catalyst (NSCL); 14wt % ¼″ × 3/16″ cylindrical diluent R2Z2 26,160 1,395 grams   100% ACS6catalyst (NSCL) Cooling 26,250 232 grams ⅜″ spherical ceramic diluentzone TOTAL 156,670 - - - - - -

The total time to produce these more than 156,000 bags was just 115.5hours, including time spent filling hoppers, programming the systemcontroller, and cleaning the system between charges—resulting in anoverall average operating speed for the system of more than 25bags/minute. Random sampling indicated that all charge weights werewithin +/−3 grams of the target weight, equivalent to not more than+/−1% by weight variability based on the total desired weight of eachbag. This demonstrates that the substantial number of catalyst chargeshaving sufficient homogeneity of amount and composition that is neededfor a commercial scale reaction system can be quickly and efficientlyproduced using the method of the present invention.

Example 6a

The inventive method can be used to prepare a “hybrid” catalyst blendcomprising 60 wt % ACF7 catalyst (available from NSCL) and 40 wt %YX-129 catalyst (available from Nippon Kayaku), both of which aresuitable catalysts for use in the first reaction stage of a propyleneoxidation reactor. Such a “hybrid” catalyst blend would be suitable forloading into the first reaction stage of the reactor to form the singlecatalyst zone (11), in accordance with the 3-reaction zone packingschedule illustrated in FIG. 1 and discussed hereinabove. Such a hybridcatalyst blend is not available commercially, but can be producedthrough the use of a combinatorial weighing system, in accordance withthe method of the present invention. This hybrid catalyst blend would beuseful in the commercial-scale production of acrylic acid frompropylene, in the first reaction zone of the oxidation reactor, becauseit would maximize desirable features such as catalyst service life andselectivity of one of the commercial catalysts, while minimizingundesirable features such as molybdenum sublimation in the othercommercial catalyst. It is envisioned that similar blends ranging fromabout 40 to 75 wt % ACF7 catalyst might also be beneficially utilized inthe first reaction stage of the 3-reaction zone packing scheduleillustrated in FIG. 1.

Example 6b

The inventive method can be used to prepare a “hybrid” catalyst blendcomprising 50 wt % YX-38 catalyst (available from Nippon Kayaku) and 50wt % ACF4 catalyst (available from NSCL), both of which are suitablecatalysts for use in the first reaction stage of a propylene oxidationreactor. Such a “hybrid” catalyst blend would be suitable for loadinginto single catalyst zone (11) in accordance with the 3-reaction zonepacking schedule illustrated in FIG. 1. Such a hybrid catalyst blend isnot available commercially, but can be produced through the use of acombinatorial weighing system, in accordance with the method of thepresent invention. This hybrid catalyst blend would be useful in thecommercial-scale production of acrylic acid from propylene as itmaximizes desirable features such as catalyst service life andselectivity of one commercial catalyst, while minimizing undesirablefeatures such as molybdenum sublimation in the other commercialcatalyst. It is envisioned that similar blends ranging from about 30 to70 wt % YX-38 catalyst might also be beneficially utilized in the firstreaction stage of the 3-reaction zone packing schedule illustrated inFIG. 1.

1. A method for blending solid materials to be placed in the tubes of ashell and tube reactor, said method comprising: (A) identifying apacking schedule which lists the types and amounts of solid materialsneeded to form different batches of solid materials for arranging in thetubes and forming desired regions in the shell and tube reactor, whereineach of said batches comprises one or more materials selected from thegroup consisting of: solid catalyst materials, solid inert materials,and blends thereof; (B) using a combinatorial weighing machine toproduce at least one of the different batches, wherein types and amountsof solid catalyst materials and solid inert materials blended for eachbatch of solid materials are selected based on the packing schedule; (C)collecting at least one of the batches of solid materials in a pluralityof containers, wherein each container of said plurality contains thesame amount and proportion of the one or more solid materials, saidamount being determined based upon the packing schedule, and each ofsaid plurality comprising a total number of containers, said totalnumber being determined by the number and size of the tubes of the shelland tube reactor; and
 2. The method according to claim 1, furthercomprising: (D) loading said batches of solid materials from each ofsaid containers into corresponding tubes of the shell and tube reactor,according to a predetermined order dictated by the packing schedule, toform said desired regions within the reactor which are consistent andhomogeneous.
 3. The method according to claim 1, wherein thecombinatorial weighing machine comprises adjustable vibrating means forchanging the rate at which solid materials are moved through the machineand blended with one another.
 4. The method according to claim 1,wherein the combinatorial weighing machine comprises dust collectionmeans for collecting and removing dust from the solid materials, therebypreventing unwanted accumulation of dust in the tubes of the shell andtube reactor.
 5. The method according to claim 1, wherein the containersare bags and a bagging machine is used with the combinatorial weighingmachine to accomplish the step of collecting each of the batches ofsolid materials in a plurality of containers.
 6. The method according toclaim 2, wherein the step of loading the batches of solid materials fromeach of said containers into corresponding tubes of the shell and tubereactor is accomplished using a solids loading machine having one ormore tubular members aligned with corresponding tubes of the shell andtube reactor.
 7. The method according to claim 1, wherein the packingschedule provides a list of types and amounts of materials required toperform two-stage oxidation of an alkene to form a correspondingunsaturated carboxylic acid, and wherein the desired regions comprise afirst reaction stage wherein the alkene is converted to an unsaturatedaldehyde and a second reaction stage wherein the unsaturated aldehyde isfurther converted to the corresponding unsaturated carboxylic acid. 8.The method according to claim 7, wherein the first reaction stagecomprises at least one catalyst comprising a mixed metal oxide and beingcapable of catalyzing the conversion of an alkene to an unsaturatedaldehyde, and the second reaction stage comprises at least one catalystcomprising a mixed metal oxide and being capable of catalyzing theconversion of an unsaturated aldehyde to an unsaturated carboxylic acid.9. The method according to claim 8, wherein said first reaction stagecomprises a plurality of reaction zones.
 10. The method according toclaim 8, wherein said second reaction stage comprises a plurality ofreaction zones.
 11. The method according to claim 8, where theunsaturated carboxylic acid comprises (meth)acrylic acid.
 12. The methodaccording to claim 1, wherein the packing schedule provides a list oftypes and amounts of materials required to produce vinyl acetate monomerfrom reactants comprising ethylene, oxygen and acetic acid.
 13. Themethod according to claim 5, wherein said amount of solid materials ineach bag varies from bag to bag by not more than +/−1% by weight basedon the total weight of each bag.
 14. The method according to claim 1,wherein the batches of solid materials are loaded into the tubes of theshell and tube reactor at a drop rate of not more than 30 seconds perliter.
 15. The method of claim 1, wherein at least one of said batchesof solid materials comprises a blend of two or more solid catalystmaterials having the same essential components but different catalyticactivity.
 16. The method of claim 1, wherein at least one of saidbatches of solid materials comprises a blend of at least one solid inertmaterial and at least one solid catalyst material.
 17. The method ofclaim 15, wherein said same essential components of the solid catalystmaterials comprise molybdenum, bismuth and iron.